Multiple disclosures have been made regarding the composition and use of various forms of biopolymer nanoparticles. For instance, U.S. Pat. No. 6,677,386 (which corresponds to WO 00/69916) describes a process for producing biopolymer nanoparticles, which in one form are starch nanoparticles. In the process, the biopolymer is plasticized using shear forces, and a crosslinking agent is added during the processing. After the processing, the biopolymer nanoparticles can be dispersed in an aqueous medium. One version of the process results in starch nanoparticles which are characterized by an average particle size of less than 400 nanometers. The nanoparticles can be used as a matrix material wherein the matrix material may be a film-forming material, a thickener, a rheology modifier, an adhesive or an adhesive additive (tackifier). The nanoparticles or dispersions thereof may also be used for their barrier properties, as a carrier, fat replacer or medicament for mitigating dermal disorders. Further examples of applications for the nanoparticles or dispersions thereof are in the paper-making and packaging industry, agriculture and horticulture fields. The nanoparticles can also be used as excipients or carriers in medicines, where they may be complexed or covalently coupled to active substances such as slow-release drugs. The nanoparticles can also be processed into a foam at relatively high density.
Other uses of the nanoparticles of U.S. Pat. No. 6,677,386 can be found in: (i) U.S. Pat. No. 7,160,420 which describes the use of the starch nanoparticles as a wet-end additive in papermaking pulp slurry, or applied to the surface of the paper as a surface sizing agent; (ii) U.S. Pat. No. 6,825,252 which describes the use of the starch nanoparticles in a binder in a pigmented paper coating composition; (iii) U.S. Pat. No. 6,921,430 which describes the use of the starch nanoparticles in environmentally friendly adhesives; and (iv) U.S. Patent Application Publication No. 2004/0241382 which describes the use of the starch nanoparticles in an adhesive for producing corrugated board. The disclosure of these patents and applications, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
The invention in U.S. Pat. No. 6,677,386 relates to a process for producing biopolymer nanoparticles which in one form are starch nanoparticles characterized by an average particle size of less than 400 nanometers. The U.S. Pat. No. 6,677,386 does not anticipate, consider nor provide any motivation to use the biopolymer nanoparticles to improve printing performance, as in the current invention, nor does it anticipate performance advantages that might result therefrom.
Thus, it can be seen that the nanoparticles prepared by the process of U.S. Pat. No. 6,677,386 have numerous uses. The application of the biopolymer nanoparticle-based Biolatex™ binders of U.S. Pat. No. 6,677,836 in coated paper and paperboard was recently described in a technical article by Bloembergen et al., entitled “Paper binder performance with biobased nanoparticles. A starch-based biolatex can replace petroleum-based latex binders in papermaking”, Paper 360.degree.Magazine, September 2008. The biolatex binder provides a high performance substitute to the petrochemical-based binders used in coated paper and paperboard manufacturing processes at a lower cost per pound. Carboxylated styrene butadiene (SB latex) and styrene acrylate (SA latex) are the dominant petrochemical-based binders used in coated paper and paperboard manufacturing.
Currently, the industry consumes over 4 billion pounds of SB and SA latex per annum. As the price of oil continues to escalate, and as the price of synthetic binders has increased by more than 100% over the past few years, paper producers have faced increased production costs forcing them to find efficiencies, pass increases on to the consumer, or cease production.
The biolatex binder of U.S. Pat. No. 6,677,836 provides performance that is comparable to SB and SA latex for important paper properties such as coating gloss, brightness, whiteness, fluorescence, ink gloss, and printability, while providing superior performance to SB and SA Latex for water retention, opacity, dry pick, print mottle, porosity (blister resistance) and paper stiffness. However, the biopolymer nanoparticles invention of U.S. Pat. No. 6,677,836 do not anticipate, consider nor provide any motivation for use in improved printing performance, as in the current invention, nor does it anticipate the significant performance advantages that result therefrom.
For instance, it is well known in the art that one area of performance deficiency relative to petro-based latex binders is in offset printing applications where water-based fountain solutions in combination with the tacky inks used in commercial 4-color offset printing operations can lead to “wet-picking” damage of the paper coating layer. The inherent challenge in meeting acceptable water-resistance is because the carbohydrate base of the biolatex binder technology is obviously more water-sensitive than the more hydrophobic petro-based binders. However, in other applications such as ink jet and flexographic printing, for example, the ability to attract water into the paper coating can be a major challenge.
Accordingly, a need exists for methods of printing which accommodate this challenge.